The present invention relates generally to a molding machine, and more particularly to a molding machine having a novel device for opening and closing the mold.
In molding machnes, such as injection molding machines, devices must be provided for opening and closing the mold space. For this purpose it is known to provide a double-acting hydraulic cylinder and piston unit the piston rod of which extends out of the cylinder and moves the movable portion of the mold to or from closed position. In the conventional apparatuses of this type pressure fluid is admitted into the pressure space of the cylinder, to thereby move the piston and piston rod to a position in which the mold is closed and the movable component of the mold transmits -- under the pressure exerted by the pressure fluid -- a closing force to the mold. The force required for subsequently opening the mold when the molding operation is completed, is exerted by admitting pressure fluid into a chamber of the cylinder which is remote from the pressure chamber, that is the second chamber formed in the cylinder by the presense of the piston. Problems are, however, encountered in these prior-art constructions because it is necessary to provide two seals or packings which must seal the piston with respect to the two pressure chambers in the cylinder. Practical experience has shown that the packings used for this purpose are subject to particularly strong wear, which is disadvantageous for a variety of reasons. On the one hand, such packings are relatively complicated and quite expensive because they must provide for a sealing effect in both direcitons that is they must seal each chamber from the other chamber. On the other hand, it is relatively difficult to gain access to these packings for the purpose of replacing them with new ones when excessive wear has developed and this, in turn, means relatively long down-time for the entire machine, since the machine obviously cannot operate during the replacement of the packings. This is economically highly undesirable.